The present invention pertains to a method and apparatus for producing a foam or cellular, plastic product, particularly a foamed plastic product having enhanced fire resistance, and products produced by that method and apparatus.
Foam plastics can be prepared by a variety of methods including, for example, an expansion process which includes expanding a fluid polymer phase to a low density cellular state and then preserving this state. A variety of manufacturing processes have been developed to achieve the steps required in an expansion process which typically include creating cells in the fluid or plastic phase, causing the cells to grow to a desired volume and stabilizing the cellular structure by physical and/or chemical means. The growth of the cells depends on the pressure differential between the cells and the environment and growth can be achieved either (a) by lowering the pressure of the external environment (decompression) or (b) by increasing the internal pressure in the cells (pressure generation) or (c) a combination of both.
Foamable compositions in which the pressure within the cells is increased relative to that of the surrounding environment have generally been called expandable formulations. Polystyrene is one of many materials used in the formation of a foam plastic in an expandable formulation process coupled with a physical stabilization process. One technique features the polymerizing of a styrene monomer in the presence of a blowing agent so that the blowing agent is entrapped in a polymerized bead. Typical blowing agents used in such processes are the various isomeric pentanes and hexanes, halocarbons, and mixtures of these materials.
The fabrication of these expandable particles into a finished cellular-plastic article is generally carried out in two steps. In the first step, the particles are expanded by means of steam, hot water, or hot air into low density replicas of the original material, called prefoamed or preexpanded beads. After proper aging, enough of these prefoamed beads are placed in a mold to just fill it; the filled mold is then exposed to steam. This second expansion of the beads causes them to flow into the spaces between beads and fuse together, forming an integral molded piece. Stabilization of the cellular structure is accomplished by cooling the molded article while it is still in the mold. The density of the cellular article can be adjusted by varying the density of the prefoamed particles.
Polyvinyl chloride and polyethylene are just a few examples of other materials, usually in beaded form, that are used in an expansion formulation process coupled with a physical stabilization process (e.g., cooling).
Another common cellular foam often used in an expansion formulation process is polyurethane. However, the cell growth of polyurethane is often controlled, at least for the most part, by a chemical stabilization process rather than relying solely on a physical stabilization process. The general method of producing cellular polyurethane is to mix a polyfunctional isocyanate with a hydroxyl-containing polymer along with the catalyst necessary to control the rate and type of reaction and typically other additives to control the surface chemistry of the process and to adjust the conditions and reactants such that the exotherm of the reaction causes expansion of the foam considerably.
Other processes for forming cellular products include decompression processes such as extrusion and injection molding. Again, either physical or chemical methods may be used to stabilize products of the decompression process. Provided below are just some examples of forming cellular product formations which include the use of decompression expansion techniques with polystyrene used as a polymer example.
Extruded polystyrenexe2x80x94A solution of blowing agent in molten polymer is formed in an extrusion under pressure and then released such that the blowing agent vaporizes and causes the polymer to expand. As an alternative to introducing a solution of blowing agent, polystyrene beads or pellets containing pentane blowing agent has been used particularly for forming low density, extruded foam sheets.
Injection Molding Polystyrenexe2x80x94Polystyrene granules containing dissolved liquid or gaseous blowing agents are used as feed in a conventional injection-molding process. With close control of time and temperature in the mold and use of vented molds, high density cellular polystyrene molding can be obtained.
Another example of a plastic foam formation process is found in a reaction injection molding or RIM process wherein polyurethane structural foam products are formed by metering into a temperature controlled mold a polyol and isocyanate to generally fill 20% to 60% of the mold depending on the density of the structural foam parts. When the reaction mixture then expands to fill the mold cavity, it forms a component part with an integral, solid skin and a microcellular core.
The foregoing represents just a few examples of the numerous processes used in the industry to form foam plastic products.
Coupled with the expanded use of foam bodies in a variety of fields, there has also been activity in the development of foam component structures having some degree of fire resistance. The prior art techniques include, for instance, providing a higher density, thickened outer layer or skin (e.g., see U.S. Pat. No. 4,191,722 with its thick-skinned roofing panels said to improve fire resistance). Another technique involves protecting the foam core with a fire retardant outer covering such as in U.S. Pat. No. 3,991,252, with protective fire retardant Gypsum layer. U.S. Pat. No. 4,136,215 describes the layering of a thin, continuous layer of inert particulate material under a still curing thermosetting foam layer (e.g., clay, sand, etc.) such that the particulate material penetrates to some extent and adheres to the foam material.
The prior art also describes the introduction of fire resistant material into the original precursors or ingredients being used in the formation of foam material used in products. These flame retardant additives which retard the surface spread of flames include, for example, halogenated materials, antimony trioxide, alumina trihydrate, borates and phosphates (see, for example, U.S. Pat. No. 4,366,204 directed at polyurethane and polyisocyanate rigid foam panels). The introduction of the flame retardant material in with the original precursors does facilitate a wide dispersion of the flame retardant material. However, in large quantities, the flame retardant material can preclude proper formation of the final product or degrade the quality of the product (particularly for situations where the required flame retardation is high as the higher quantity of flame retardant material can create problems in preparing quality products with certain desired characteristics or starting materials). The inventors have determined, for example, that while the initial dispersement of flame additives (e.g., boron) in with reactive foam mix precursors in a die mold allows for acceptable products for car manufacturing, when dealing with sufficient flame retardant additives to satisfy building code levels proper fusing and foam formation did not occur. This was also true with respect to the initial mixing of expandable plastic beads in with fire retardant material as the amount of flame additives needed to satisfy building code levels or standardized association requirements (e.g., ASTM E 108-90xe2x80x94xe2x80x9cStandard Test Methods for Fire Tests of Roof Coveringsxe2x80x9d and ANSI/UL (Underwriters Lab, Inc.) 790xe2x80x94DEVELOPMENTAL SPREAD OF FLAME TEST, which are incorporated herein by reference in their entirety), would result in unacceptable products. That is, the blending of fire retardant materials with expanded plastic beads prior to the molding process failed to produce an acceptable fire retardant foam product either due to the product not properly forming or the failure to satisfy the requirements in, for example, the Class A level of the aforementioned ANSI/UL 790 Test.
Among other things, the present invention is directed at providing a plastic foam or cellular body with a high fire resistance or flame spread retardation characteristic, while also providing for proper formation of the plastic foam material to provide a high quality foam product.
The advantageous features of the present invention include a foam body structure having a foam body with one or more flame retardant reception cavities formed therein and a flame retardant material received by said one or more flame retardant cavities with the cavity arrangement and flame retardant dispersion being sufficient in the foam body to satisfy, for example, established fire resistance building code levels and applicable association standards and the like, such as the fire test requirements set out in ASTM E 108-90 or ANSI/UL 790. The method of the present invention includes the formation of reception cavities commensurate with the formation of the foam product as well as the formation of reception cavities after formation of the foam product. Thus, the present invention is applicable to a wide variety of foam production methods. The present invention, particularly from the standpoint of formation of reception cavities commensurate with foam body formation, is particularly well suited for use in conjunction with plastic foam products produced through mixed liquid precursors (causing the crosslinking of a thermosetting resin; such as polyester resin, concurrently with the production of carbon dioxide by the reaction of a carbonite with an inorganic acid) and the formation of formed molten plastic particles from expandable plastic particles such as copolymer beads having a polymer outer coating, and a blower core of pentane or the like. The present invention, with its high fire resistivity characteristics, is also particularly well suited for the production of foam body construction items such as shingles and wall panels and also as wood substitutes for furniture and other furnishings.
Under one technique of the present invention, following full formation of the expanded foam body, a repeating pattern of flame retardant reception cavities are formed in the foam body. The reception cavities are sufficiently dispersed in (and/or over) the foam body and sufficiently sized as to provide a sufficient number and size of cavities to receive enough flame retardant additive material to pass the upper level requirements (e.g., Class A) of standardized fire resistance tests such as the aforementioned ANSI/UL 790 and ASTM E 108 90 Tests. The flame retardant additive is provided to the reception cavities preferably either in solid, liquid, or gaseous form or a combination thereof. A variety of sealing techniques for encapsulating the flame retardant material within the reception cavities are used in the present invention, particularly when using solid inhibitors (e.g., granular, tablet or powder form). A standard coating or laminate layer used in the field can be used as an encapsulator and can be one that either has or does not have an added flame retardant quality as the material in the reception cavities is preferably capable of meeting the aforementioned standards in and of itself for most foam body structures and intended uses thereof.
As the above described Tests require the whole component or article to meet the particular requirements set forth, the reception cavity (or reception cavities are) is preferably sufficiently spread over the surface of the foam body to allow for a uniform fire resistance over the entire foam body in the aggregate. That is, enough fire retardant additive is provided such that when the product is subjected to a flame, there is sufficient fire retardant distribution to cover 100% of the product (i.e., to prevent the product from burning or flames from spreading over the entire volume of the product within the requirements of, for example , the aforementioned ANSI/UL 790 Test).
The reception cavities include, for example, repeating rows of spaced reception cavities that are in the form of vertical holes having a top end opening out at an exterior surface of said foam body and a closed off bottom end. Holes such as frusto-conical holes that extend through 25% to 95%, and more preferably 75% to 95%, of a vertical thickness of said foam body are suitable for use in the present invention.
Another embodiment of the present invention features a plurality of reception cavities that are formed in the foam body so as to extend internally within the foam body below an upper or first surface of a body and above a lower or second surface of said foam body such as reception cavities that include a first series of cavities (e.g., cylindrical) extending between two side walls of a foam body so as to leave the upper end lower surface of the foam body undisturbed or an additional second series of cavities (e.g., cylindrical) that intersect with the first series or cavities or lie on a different plane between the exposed top and bottom of the foam body. The flame retardant material is received in said one or more reception cavities. The number and size of cavities is dependent on what particular fire retardant level is needed to pass the particular test requirement desired for passing, such as the above noted ANSI/UL 790 and ASTM E 180 90 standards, while taking into consideration the material of the plastic involved and any added material such as any added laminate or the like.
Another embodiment of the present invention features a retardant reception cavity arrangement that includes one or a plurality of slits or grooves formed in an exposed surface of said foam body with the grooves or slits extending down for a depth greater than 50% of a vertical thickness of said foam body.
The foam body structure can further comprise a covering positioned over the reception cavities such as a conforming covering layer of a standard hardenable liquid coating which comes in contact with the flame retardant material within said one or more reception cavities, the foam material bordering said one or more reception cavities, and possibly a portion of the foam body defining the reception cavity depending on whether the reception cavity is entirely filled or only partially filled by the flame retardant material. Alternatively, a less conforming laminate is joined to an exposed surface of said foam body within which flame retardant reception cavities are formed and extends over the surface openings formed in said foam body which are defined by the plurality of flame retardant reception cavities. A joining agent provided on the bordering regions and/or provided on the laminate""s contacting surface and/or within said reception cavities can also be used to bond a laminate over the foam body so as to cover a film or pile of the flame retardant material received within said one or more reception cavities. The laminate or coating can also be provided with added fire retardant material or be of a type that inherently is fire retardant. Alternatively, the laminate can be of a type that is not fire retardant or actually promotes flame spread on its own, were it not for the flame retardant function of the material in the main foam body.
The present invention also features a method of forming a flame retardant plastic foam body structure, comprising introducing flame retardant material into one or more flame retardant material reception cavities formed in a foam body such that the flame retardant material is dispersed over a sufficient volume of the foam body to achieve a high fire retardant quality. The flame retardant material is evenly dispersed to ensure an essentially equal fire retardant characteristic over the entire volume of the foam body. For example, the reception cavities are of a sufficient volume and sufficiently dispersed so that when the reception cavities are filled or provided with the desired amount and type of fire retardant material, the flame retardation quality of the foam body is common over the entire foam body in that a flame applied to any location of the foam body will be subject to essentially equal retardation, particularly from the standpoint of flame spread parameters like those found in the above-noted ASTM E 180 90 and ANSI/UL 790 standards.
The method of the present invention preferably includes introducing flame retardant material into said one or more flame retardant reception cavities which is or are distributed over essentially all of at least one exposed surface of said foam body or internalized within the interior of the foam body.
The introduction of the flame retardant also includes introducing flame retardant to the flame retardant reception cavities which flame retardant reception cavities often need only constitute about 0.5 to 10% of the total volume of the foam body with the total volume represented by both the body of foam material and the cavities within the foam body. The 0.5 to 10% range is representative of an amount of volume needed for the fire retardant material to achieve the above noted goals of satisfying both a high quality fire retardant level (e.g., Class A of ANSI/UL 790) and also to provide equal protection at that level across the entire foam body. However, this volume range may vary either above or below depending on the particular foam material and retardant(s) utilized. Also, the number and volume of cavities can be varied to achieve the desired effect. That is, a lesser amount of larger volume cavities, as opposed to a greater number of lower volume cavities, may be more desirable, in some instances, to provide, for example, sufficient flame retardant material which is sufficiently dispersed throughout the foam body to provide sufficient fire-retardation or resistance as to pass the Class A developmental spread of Flame Test ANSI/UL 790 and similar test levels for a variety of possible products produced in accordance with the present invention (e.g., roof shingles, wall panels, and wood substitutes for furniture).
The method of the present invention includes the formation of the foam body prior to flame retardant application. For example, the foam body can be formed in a molding process, wherein the flame retardant reception cavities are formed in the foam body during the molding of the foam body. Additionally, a cover layer can be applied to the foam body following the introduction of the flame retardant material. A variety of different flame retardant materials can be utilized in the present invention both in regard to chemical composition and state. For example, a solid fire retardant material in, for example, powdered, granular, or tablet form, can be inserted into the formed cavities, preferably in a firm, packed state, and either covered or coated so as to retain its initial, relative position. Preferably, the size of the holes or reception cavities is minimized such that the quantity of solid flame retardant material fills the entire volume of each cavity. The cavities can also be partially filled if, for example, greater depth penetration is desired to help in the distribution of flame retardant so as to protect the entire volume of the foam body and wherein the flame retardant material is sufficiently effective as to not require complete filling of the holes. A variety of different depth holes, some entirely filled, some filled to different levels, can also be utilized for dispersement purposes.
The method of the present invention further includes providing cover material that is in fluid or flowable (e.g., a gel) form at the time of application and thus provides a coating cover that conforms to the surface configuration of said foam body and the upper surface of the fire retardant material in the reception cavities whether filled or not. Alternatively, or in combination with, a rigid or flexible (but not necessarily aperture conforming if the reception cavities are not entirely filled) laminate sheet extends over the one or more openings defined by said flame retardant reception cavities formed in said foam body. Particularly for forming larger fire retardant foam bodies, individual foam bodies having the fire retardant material aperture(s) can be stacked or otherwise joined together, preferably with at least one of the foam bodies covering over the apertures of another foam body.
The present invention also includes an assembly for forming a foam body with at least one flame retardant reception cavity comprising a foam material reception device with mold or article defining cavity and one or more flame retardant cavity formation members extending or positioned within said mold or article defining cavity for forming one or more grooves, holes or cavities in the body. The combination of a mold or foam material reception device and one or more flame retardant reception cavity forming members represents a modified molding system that is well suited for use in any one of the numerous techniques used in forming foam bodies, some of which are described in the background portion of the present invention. For example, the specially designed mold cavity with fire resistant material reception cavity forming means can receive the polymer material to be used in the production of the foam body from a variety of sources such as high pressure injection or extrusion feeding systems or from lower pressure systems for introducing to-be-expanded polymer material (e.g., air stream injected expandable beads or foam precursors to merge together in the mold reception cavity).
The aforementioned assembly also includes, in one embodiment of the invention, a flame retardant supply assembly opening into the mold cavity wherein said supply assembly has nozzle members or material directing means extending directly over or into the one or more flame retardant cavity formation locations in the foam body. Suitable shut off valves or the like can be used to terminate a flow of flame retardant material into a reception cavity when the desired quantity of material has passed into the reception cavity. This can include, for example, a sliding plate valve when a solid flame retardant is being supplied or a fluid shut off valve when a liquid fire retardant supply (e.g., liquid with solid particle suspension) or a gaseous flame retardant (e.g., fine powder flame retardant suspended in a gaseous delivery system) is involved.
Another feature of the invention involves a device and method for forming the desired number and size of reception cavities within an already formed foam body. This can include, for example, a support for a foam body that has reached a set-up state wherein its cells have stabilized over its entire body or essentially its entire body (e.g., sufficient setup so that cavities can be formed by an applied cavity forming means without the necessity of an encompassing mold structure to retain the shape of the foam body material to remain after cavity removal). The device and method for forming the flame retardant cavities prior to the adding of fire retardant material and after a foam body molding process is complete, can take on a variety of forms such as means for forming one or more grooves, holes or cavities by, for example, punching, routing, boring, cutting, drilling, sawing, melting or any other acceptable method.